Hardwood pulp fiber-containing structures and methods for making same

ABSTRACT

Hardwood pulp fiber-containing structures, more particularly to eucalyptus pulp fiber-containing fibrous structures that may exhibit improved fiber densification and/or improved softness compared to known hardwood pulp fiber-containing fibrous structures are provided.

FIELD OF THE INVENTION

The present invention relates to hardwood pulp fiber-containing structures, more particularly to hardwood pulp fiber-containing fibrous structures that exhibit improved fiber densification and/or improved softness compared to known hardwood pulp fiber-containing fibrous structures. In one example, the present invention relates to hardwood pulp fiber-containing fibrous structures comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of hardwood pulp fibers that exhibit desired fiber properties and methods for making same.

BACKGROUND OF THE INVENTION

Hardwood pulp fiber-containing fibrous structures are known in the art. For example, the inclusion of commercially available eucalyptus pulp fibers and/or blends thereof, such as those commercially available from Fibria in Brazil under the trade name bleached eucalyptus kraft or BEK and Suzano Pulp and Paper in Brazil under the trade name Suzano Mucuri (a blend of eucalyptus pulp fibers). In addition to eucalyptus pulp fibers, fibrous structures comprising acacia pulp fibers, such as those commercially available from Riaupulp in Indonesia are also known in the art. Further, northern hardwood pulp fibers, such as maple pulp fibers, are also known to be used in fibrous structures.

However, consumers of hardwood pulp fiber-containing fibrous structures continue to desire new and/or improved properties from hardwood pulp fibers contained within fibrous structures.

Accordingly, there is a need for hardwood pulp fiber-containing fibrous structures and/or hardwood pulp fibers-contained within such fibrous structures that exhibit new and/or improved properties compared to known fibrous structures and methods for making same.

SUMMARY OF THE INVENTION

The present invention fulfills the needs described above by providing one or more hardwood pulp fibers and/or hardwood pulp fiber compositions that exhibit desired fiber properties that are suitable for use in producing fibrous structures according to the present invention.

In one example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of hardwood pulp fibers that exhibit a Kajaani fiber width of less than 13.90 μm, is provided.

In another example of the present invention, a single- or multi-ply sanitary tissue product comprising a fibrous structure according to the present invention, is provided.

In still another example of the present invention, a method for making a fibrous structure according to the present invention comprises the steps of:

-   -   a. providing a fibrous furnish comprising 1% and/or 3% and/or 5%         or greater, for example greater than 5%, by weight of hardwood         pulp fibers that exhibit a Kajaani fiber width of less than         13.90 μm;     -   b. depositing the fibrous furnish on a foraminous forming         surface to form an embryonic fibrous web;     -   c. drying the embryonic fibrous web such that the fibrous         structure is formed, is provided.

In yet another example of the present invention, a hardwood pulp fiber composition comprising:

-   -   a. 20% or greater by weight of hardwood pulp fibers that exhibit         a Kajaani fiber width of less than 13.90 μm; and     -   b. 80% or less by weight of hardwood pulp fibers that exhibit a         Kajaani fiber width of 13.90 μm or greater, is provided.

In yet another example of the present invention, a hardwood pulp fiber composition comprising:

-   -   a. 20% or greater by weight of hardwood pulp fibers that exhibit         a Kajaani fiber cell wall thickness of less than 5.98 μm; and     -   b. 80% or less by weight of hardwood pulp fibers that exhibit a         Kajaani fiber cell wall thickness of 5.98 μm or greater, is         provided.

In yet another example of the present invention, a hardwood pulp fiber composition comprising:

-   -   a. 20% or greater by weight of hardwood pulp fibers that exhibit         a Kajaani millions of fibers/gram of greater than 24 millions of         fibers/gram; and     -   b. 80% or less by weight of hardwood pulp fibers that exhibit a         Kajaani millions of fibers/gram of 24 millions of fibers/gram or         less, is provided.

In yet another example of the present invention, a eucalyptus pulp fiber composition comprising:

-   -   a. 20% or greater by weight of eucalyptus pulp fibers that         exhibit a Kajaani fiber width of less than 14.15 μm; and     -   b. 80% or less by weight of eucalyptus pulp fibers that exhibit         a Kajaani fiber width of 14.15 μm or greater, is provided.

In yet another example of the present invention, a eucalyptus pulp fiber composition comprising:

-   -   a. 20% or greater by weight of eucalyptus pulp fibers that         exhibit a Kajaani fiber cell wall thickness of less 6.15 μm; and     -   b. 80% or less by weight of eucalyptus pulp fibers that exhibit         a Kajaani fiber cell wall thickness of 6.15 μm or greater, is         provided.

In yet another example of the present invention, a eucalyptus pulp fiber composition comprising:

-   -   a. 20% or greater by weight of eucalyptus pulp fibers that         exhibit a Kajaani millions of fibers/gram of greater than 20.5         millions of fibers/gram; and     -   b. 80% or less by weight of eucalyptus pulp fibers that exhibit         a Kajaani millions of fibers/gram of 20.5 millions of         fibers/gram or less, is provided.

In yet another example of the present invention, a process for making a hardwood pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a hardwood pulp fiber composition comprising less         than 20% by weight of hardwood pulp fibers that exhibit a         Kajaani fiber width of less than 13.90 μm and greater than 80%         by weight of hardwood pulp fibers that exhibit a Kajaani fiber         width of 13.90 μm or greater;     -   b. adjusting the weight percents of the hardwood pulp fibers         such that a hardwood pulp fiber composition comprising         -   i. 20% or greater by weight of hardwood pulp fibers that             exhibit a Kajaani fiber width of less than 13.90 μm; and         -   ii. 80% or less by weight of hardwood pulp fibers that             exhibit a Kajaani fiber width of 13.90 μm or greater is             formed, is provided.

In yet another example of the present invention, a process for making a eucalyptus pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a eucalyptus pulp fiber composition comprising less         than 20% by weight of eucalyptus pulp fibers that exhibit a         Kajaani fiber width of less than 14.15 μm and greater than 80%         by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber         width of 14.15 μm or greater;     -   b. adjusting the weight percents of the eucalyptus pulp fibers         such that a eucalyptus pulp fiber composition comprising         -   i. 20% or greater by weight of eucalyptus pulp fibers that             exhibit a Kajaani fiber width of less than 14.15 μm; and         -   ii. 80% or less by weight of eucalyptus pulp fibers that             exhibit a Kajaani fiber width of 14.15 μm or greater is             formed, is provided.

In yet another example of the present invention, a process for making a hardwood pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a hardwood pulp fiber composition comprising less         than 20% by weight of hardwood pulp fibers that exhibit a         Kajaani fiber cell wall thickness of less than 5.98 μm and         greater than 80% by weight of hardwood pulp fibers that exhibit         a Kajaani fiber cell wall thickness of 5.98 μm or greater;     -   b. adjusting the weight percents of the hardwood pulp fibers         such that a hardwood pulp fiber composition comprising         -   i. 20% or greater by weight of hardwood pulp fibers that             exhibit a Kajaani fiber cell wall thickness of less than             5.98 μm; and         -   ii. 80% or less by weight of hardwood pulp fibers that             exhibit a Kajaani fiber cell wall thickness of 5.98 μm or             greater is formed, is provided.

In yet another example of the present invention, a process for making a eucalyptus pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a eucalyptus pulp fiber composition comprising less         than 20% by weight of eucalyptus pulp fibers that exhibit a         Kajaani fiber cell wall thickness of less than 6.15 μm and         greater than 80% by weight of eucalyptus pulp fibers that         exhibit a Kajaani fiber cell wall thickness of 6.15 μm or         greater;     -   b. adjusting the weight percents of the eucalyptus pulp fibers         such that a eucalyptus pulp fiber composition comprising         -   i. 20% or greater by weight of eucalyptus pulp fibers that             exhibit a Kajaani fiber cell wall thickness of less than             6.15 μm; and         -   ii. 80% or less by weight of eucalyptus pulp fibers that             exhibit a Kajaani fiber cell wall thickness of 6.15 μm or             greater is formed, is provided.

In yet another example of the present invention, a process for making a hardwood pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a hardwood pulp fiber composition comprising less         than 20% by weight of hardwood pulp fibers that exhibit a         Kajaani millions of fibers/gram of greater than 24 millions of         fibers/gram and greater than 80% by weight of hardwood pulp         fibers that exhibit a Kajaani millions of fibers/gram of 24         millions of fibers/gram or less;     -   b. adjusting the weight percents of the hardwood pulp fibers         such that a hardwood pulp fiber composition comprising         -   i. 20% or greater by weight of hardwood pulp fibers that             exhibit a Kajaani millions of fibers/gram of greater than 24             millions of fibers/gram; and         -   ii. 80% or less by weight of hardwood pulp fibers that             exhibit a Kajaani millions of fibers/gram of 24 millions of             fibers/gram or less is formed, is provided.

In yet another example of the present invention, a process for making a eucalyptus pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a eucalyptus pulp fiber composition comprising less         than 20% by weight of eucalyptus pulp fibers that exhibit a         Kajaani millions of fibers/gram of greater than 20.5 millions of         fibers/gram and greater than 80% by weight of eucalyptus pulp         fibers that exhibit a Kajaani millions of fibers/gram of 20.5         millions of fibers/gram or less;     -   b. adjusting the weight percents of the eucalyptus pulp fibers         such that a eucalyptus pulp fiber composition comprising         -   i. 20% or greater by weight of eucalyptus pulp fibers that             exhibit a Kajaani millions of fibers/gram of greater than             20.5 millions of fibers/gram and         -   ii. 80% or less by weight of eucalyptus pulp fibers that             exhibit a Kajaani millions of fibers/gram of 20.5 millions             of fibers/gram or less is formed, is provided.

In yet another example of the present invention, a process for making a eucalyptus pulp fiber composition according to the present invention comprises the steps of:

-   -   a. providing a eucalyptus pulp fiber composition comprising less         than 20% by weight of eucalyptus pulp fibers that exhibit a         Kajaani fiber coarseness of less than 0.074 mg/m and greater         than 80% by weight of eucalyptus pulp fibers that exhibit a         Kajaani fiber coarseness of 0.074 mg/m or greater;     -   b. adjusting the weight percents of the eucalyptus pulp fibers         such that a eucalyptus pulp fiber composition comprising         -   i. 20% or greater by weight of eucalyptus pulp fibers that             exhibit a Kajaani fiber coarseness of less than 0.074 mg/m;             and         -   ii. 80% or less by weight of eucalyptus pulp fibers that             exhibit a Kajaani fiber coarseness of 0.074 mg/m or greater             is formed, is provided.

In even another example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of hardwood pulp fibers that exhibit a Kajaani fiber cell wall thickness of less than 5.98 μm and/or less than 5.96 μm and/or less than 5.94 μm, is provided.

In even yet another example of the present invention, a fibrous structure comprising about 5% or greater by weight of hardwood pulp fibers that exhibit a Kajaani millions of fibers/gram of greater than 24 millions of fibers/gram and/or greater than 24.5 millions of fibers/gram and/or greater than 25 millions of fibers/gram, is provided.

In still another example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber width of less than 14.15 μm and/or less than 14.10 μm and/or less than 14.05 μm and/or less than 14.00 μm and/or less than 13.95 μm and/or less than 13.90 μm, is provided.

In still yet another example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber cell wall thickness of less than 6.15 μm and/or less than 6.10 μm and/or less than 6.05 μm and/or less than 6.00 μm and/or less than 5.98 μm and/or less than 5.96 μm and/or less than 5.94 μm, is provided.

In even yet another example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of eucalyptus pulp fibers that exhibit a Kajaani millions of fibers/gram of greater than 20.5 millions of fibers/gram and/or greater than 21 millions of fibers/gram and/or greater than 21.5 millions of fibers/gram and/or greater than 22 millions of fibers/gram and/or greater than 22.5 millions of fibers/gram and/or greater than 23 millions of fibers/gram and/or greater than 23.5 millions of fibers/gram and/or greater than 24 millions of fibers/gram and/or greater than 24.5 millions of fibers/gram and/or greater than 25 millions of fibers/gram, is provided.

In even still yet another example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of eucalyptus pulp fibers that exhibits a ratio of Kajaani fiber length (μm) to Kajaani fiber width (μm) of less than 45 and/or less than 43 and/or less than 41, is provided.

In even still yet another example of the present invention, a fibrous structure comprising 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of eucalyptus pulp fibers that exhibit a ratio of Kajaani fiber coarseness of less than 0.074 mg/m and/or less than 0.0735 mg/m, is provided.

The present invention provides novel hardwood pulp fiber-containing fibrous structures, hardwood pulp fiber compositions and methods for making same.

DETAILED DESCRIPTION OF THE INVENTION

“Fiber” as used herein means an elongate physical structure having an apparent length greatly exceeding its apparent diameter, i.e. a length to diameter ratio of at least about 10. Fibers having a non-circular cross-section and/or tubular shape are common; the “diameter” in this case may be considered to be the diameter of a circle having cross-sectional area equal to the cross-sectional area of the fiber. More specifically, as used herein, “fiber” refers to fibrous structure-making fibers. The present invention contemplates the use of a variety of fibrous structure-making fibers, such as, for example, natural fibers, such as trichome fibers and/or wood pulp fibers, or synthetic fibers, or any other suitable fibers, and any combination thereof.

Natural fibrous structure-making fibers useful in the present invention include animal fibers, mineral fibers, other plant fibers (in addition to the hardwood pulp fibers of the present invention) and mixtures thereof. Animal fibers may, for example, be selected from the group consisting of: wool, silk and mixtures thereof. The other plant fibers may, for example, be derived from a plant selected from the group consisting of: wood, cotton, cotton linters, flax, sisal, abaca, hemp, hesperaloe, jute, bamboo, bagasse, kudzu, corn, sorghum, gourd, agave, loofah and mixtures thereof.

Wood fibers, often referred to as wood pulps, include chemical pulps, such as kraft (sulfate) and sulfite pulps, as well as mechanical and semi-chemical pulps including, for example, groundwood, thermomechanical pulp, chemi-mechanical pulp (CMP), chemi-thermomechanical pulp (CTMP), neutral semi-chemical sulfite pulp (NSCS). Chemical pulps, however, may be preferred since they impart a superior tactile sense of softness to tissue sheets made therefrom. Pulps derived from both deciduous trees (hereinafter, also referred to as “hardwood”) and coniferous trees (hereinafter, also referred to as “softwood”) may be utilized. The hardwood and softwood fibers can be blended, or alternatively, can be deposited in layers to provide a stratified and/or layered web. U.S. Pat. No. 4,300,981 and U.S. Pat. No. 3,994,771 are incorporated herein by reference for the purpose of disclosing layering of hardwood and softwood fibers. Also applicable to the present invention are fibers derived from recycled paper, which may contain any or all of the above categories as well as other non-fibrous materials such as fillers and adhesives used to facilitate the original papermaking.

Wood pulp fibers may be hardwood pulp fibers or softwood pulp fibers. Non-limiting examples of hardwood pulp fibers include fibers derived from a fiber source selected from the group consisting of: Acacia, Eucalyptus, Maple, Oak, Aspen, Birch, Cottonwood, Alder, Ash, Cherry, Elm, Hickory, Poplar, Gum, Walnut, Locust, Sycamore, Beech, Catalpa, Sassafras, Gmelina, Albizia, Anthocephalus, and Magnolia. Non-limiting examples of softwood pulp fibers include fibers derived from a fiber source selected from the group consisting of: Pine, Spruce, Fir, Tamarack, Hemlock, Cypress, and Cedar. Softwood pulp fibers derived from the kraft process and originating from more-northern climates may be preferred. These are often referred to as northern softwood kraft (NSK) pulps.

Synthetic fibers may be selected from the group consisting of: wet spun fibers, dry spun fibers, melt spun (including melt blown) fibers, synthetic pulp fibers and mixtures thereof. Synthetic fibers may, for example, be comprised of cellulose (often referred to as “rayon”); cellulose derivatives such as esters, ether, or nitrous derivatives; polyolefins (including polyethylene and polypropylene); polyesters (including polyethylene terephthalate); polyamides (often referred to as “nylon”); acrylics; non-cellulosic polymeric carbohydrates (such as starch, chitin and chitin derivatives such as chitosan); polylactic acids, polyhydroxyalkanoates, polycaprolactones, and mixtures thereof. In one example, synthetic fibers may be used as binding agents.

“Fiber Length”, “Average Fiber Length” and “Weighted Average Fiber Length”, are terms used interchangeably herein all intended to represent the “Length Weighted Average Fiber Length” as determined for example by means of a Kajaani FiberLab Fiber Analyzer commercially available from Metso Automation, Kajaani Finland. The instructions supplied with the unit detail the formula used to arrive at this average. The recommended method for measuring fiber length using this instrument is essentially the same as detailed by the manufacturer of the FiberLab in its operation manual. The recommended consistencies for charging to the FiberLab are somewhat lower than recommended by the manufacturer since this gives more reliable operation. Short fiber furnishes, as defined herein, should be diluted to 0.02-0.04% prior to charging to the instrument. Long fiber furnishes, as defined herein, should be diluted to 0.15%-0.30%. Alternatively, fiber length may be determined by sending the short fibers to a contract lab, such as Integrated Paper Services, Appleton, Wis.

Fibrous structures may be comprised of a combination of hardwood pulp fibers and softwood pulp fibers.

Non-limiting examples of suitable hardwood pulp fibers for use in the present invention include fibers that exhibit an average fiber length of less than about 5 mm and/or less than about 3 mm and/or less than about 1.2 mm and/or less than about 1.0 mm and/or from about 0.4 mm to about 5 mm and/or from about 0.5 mm to about 3 mm and/or from about 0.5 mm to about 1.2 mm and/or from about 0.6 mm to about 1.0 mm.

Non-limiting examples of suitable softwood pulp fibers for use in the present invention include fibers that exhibit an average fiber length of less than about 7 mm and/or less than about 5 mm and/or less than about 3 mm and/or less than about 2.5 mm and/or from about 1 mm to about 5 mm and/or from about 1.5 mm to about 3 mm and/or from about 1.8 mm to about 4 mm and/or from about 2 mm to about 3 mm.

“Fibrous structure” as used herein means a structure that comprises one or more fibers. Non-limiting examples of processes for making fibrous structures include known wet-laid papermaking processes and air-laid papermaking processes. Such processes typically include steps of preparing a fiber composition in the form of a suspension in a medium, either wet, more specifically aqueous medium, or dry, more specifically gaseous, i.e. with air as medium. The aqueous medium used for wet-laid processes is oftentimes referred to as a fiber slurry. The fibrous suspension is then used to deposit a plurality of fibers onto a forming wire or belt such that an embryonic fibrous structure is formed, after which drying and/or bonding the fibers together results in a fibrous structure. Further processing the fibrous structure may be carried out such that a finished fibrous structure is formed. For example, in typical papermaking processes, the finished fibrous structure is the fibrous structure that is wound on the reel at the end of papermaking, and may subsequently be converted into a finished product, e.g. a sanitary tissue product.

Non-limiting types of fibrous structures according to the present invention include conventionally felt-pressed fibrous structures; pattern densified fibrous structures; and high-bulk, uncompacted fibrous structures. The fibrous structures may be of a homogenous or multilayered (two or three or more layers) construction; and the sanitary tissue products made therefrom may be of a single-ply or multi-ply construction.

In one example, the fibrous structure of the present invention is a pattern densified fibrous structure characterized by having a relatively high-bulk region of relatively low fiber density and an array of densified regions of relatively high fiber density. The high-bulk field is characterized as a field of pillow regions. The densified zones are referred to as knuckle regions. The knuckle regions exhibit greater density than the pillow regions. The densified zones may be discretely spaced within the high-bulk field or may be interconnected, either fully or partially, within the high-bulk field. Typically, from about 8% to about 65% of the fibrous structure surface comprises densified knuckles, the knuckles may exhibit a relative density of at least 125% of the density of the high-bulk field. Processes for making pattern densified fibrous structures are well known in the art as exemplified in U.S. Pat. Nos. 3,301,746, 3,974,025, 4,191,609 and 4,637,859.

The fibrous structures comprising a hardwood pulp fibers in accordance with the present invention may be in the form of through-air-dried fibrous structures, differential density fibrous structures, differential basis weight fibrous structures, wet laid fibrous structures, air laid fibrous structures (examples of which are described in U.S. Pat. Nos. 3,949,035 and 3,825,381), conventional dried fibrous structures, creped or uncreped fibrous structures, patterned-densified or non-patterned-densified fibrous structures, compacted or uncompacted fibrous structures, nonwoven fibrous structures comprising synthetic or multicomponent fibers, homogeneous or multilayered fibrous structures, double re-creped fibrous structures, foreshortened fibrous structures, co-form fibrous structures (examples of which are described in U.S. Pat. No. 4,100,324) and mixtures thereof.

In one example, the air laid fibrous structure is selected from the group consisting of thermal bonded air laid (TBAL) fibrous structures, latex bonded air laid (LBAL) fibrous structures and mixed bonded air laid (MBAL) fibrous structures.

The fibrous structures may exhibit a substantially uniform density or may exhibit differential density regions, in other words regions of high density compared to other regions within the patterned fibrous structure. Typically, when a fibrous structure is not pressed against a cylindrical dryer, such as a Yankee dryer, while the fibrous structure is still wet and supported by a through-air-drying fabric or by another fabric or when an air laid fibrous structure is not spot bonded, the fibrous structure typically exhibits a substantially uniform density.

“Sanitary tissue product” as used herein means a soft, low density (i.e. <about 0.15 g/cm³) web useful as a wiping implement for post-urinary and post-bowel movement cleaning (toilet tissue), for otorhinolaryngological discharges (facial tissue), and multi-functional absorbent and cleaning uses (absorbent towels). The sanitary tissue product may be convolutedly wound upon itself about a core or without a core to form a sanitary tissue product roll.

In one example, the sanitary tissue product of the present invention comprises a fibrous structure according to the present invention.

The sanitary tissue products of the present invention may exhibit a basis weight between about 10 g/m² (“gsm”) to about 120 g/m² and/or from about 15 g/m² to about 110 g/m² and/or from about 20 g/m² to about 100 g/m² and/or from about 30 to 90 g/m². In addition, the sanitary tissue product of the present invention may exhibit a basis weight between about 40 g/m² to about 120 g/m² and/or from about 50 g/m² to about 110 g/m² and/or from about 55 g/m² to about 105 g/m² and/or from about 60 to 100 g/m² as measured according to the Basis Weight Test Method described herein.

“Basis Weight” as used herein is the weight per unit area of a sample reported in lbs/3000 ft² or g/m². Basis weight is measured by preparing one or more samples of a certain area (m²) and weighing the sample(s) of a fibrous structure according to the present invention and/or a sanitary tissue product comprising such fibrous structure on a top loading balance with a minimum resolution of 0.01 g. The balance is protected from air drafts and other disturbances using a draft shield. Weights are recorded when the readings on the balance become constant. The average weight (g) is calculated and the average area of the samples (m²) is measured. The basis weight (g/m²) is calculated by dividing the average weight (g) by the average area of the samples (m²).

“Softness” of a fibrous structure according to the present invention and/or a paper product comprising such fibrous structure is determined as follows. Ideally, prior to softness testing, the samples to be tested should be conditioned according to Tappi Method #T4020M-88. Here, samples are preconditioned for 24 hours at a relative humidity level of 10 to 35% and within a temperature range of 22° C. to 40° C. After this preconditioning step, samples should be conditioned for 24 hours at a relative humidity of 48% to 52% and within a temperature range of 22° C. to 24° C. Ideally, the softness panel testing should take place within the confines of a constant temperature and humidity room. If this is not feasible, all samples, including the controls, should experience identical environmental exposure conditions.

Softness testing is performed as a paired comparison in a form similar to that described in “Manual on Sensory Testing Methods”, ASTM Special Technical Publication 434, published by the American Society For Testing and Materials 1968 and is incorporated herein by reference. Softness is evaluated by subjective testing using what is referred to as a Paired Difference Test. The method employs a standard external to the test material itself. For tactile perceived softness two samples are presented such that the subject cannot see the samples, and the subject is required to choose one of them on the basis of tactile softness. The result of the test is reported in what is referred to as Panel Score Unit (PSU). With respect to softness testing to obtain the softness data reported herein in PSU, a number of softness panel tests are performed. In each test ten practiced softness judges are asked to rate the relative softness of three sets of paired samples. The pairs of samples are judged one pair at a time by each judge: one sample of each pair being designated X and the other Y. Briefly, each X sample is graded against its paired Y sample as follows:

1. a grade of plus one is given if X is judged to may be a little softer than Y, and a grade of minus one is given if Y is judged to may be a little softer than X;

2. a grade of plus two is given if X is judged to surely be a little softer than Y, and a grade of minus two is given if Y is judged to surely be a little softer than X;

3. a grade of plus three is given to X if it is judged to be a lot softer than Y, and a grade of minus three is given if Y is judged to be a lot softer than X; and, lastly:

4. a grade of plus four is given to X if it is judged to be a whole lot softer than Y, and a grade of minus 4 is given if Y is judged to be a whole lot softer than X.

The grades are averaged and the resultant value is in units of PSU. The resulting data are considered the results of one panel test. If more than one sample pair is evaluated then all sample pairs are rank ordered according to their grades by paired statistical analysis. Then, the rank is shifted up or down in value as required to give a zero PSU value to which ever sample is chosen to be the zero-base standard. The other samples then have plus or minus values as determined by their relative grades with respect to the zero base standard. The number of panel tests performed and averaged is such that about 0.2 PSU represents a significant difference in subjectively perceived softness.

Hardwood Pulp Fibers

The fibrous structures of the present invention comprise hardwood pulp fibers. The hardwood pulp fibers may comprise tropical hardwood pulp fibers. In another example, the hardwood pulp fibers comprise eucalyptus pulp fibers. The fiber properties disclosed herein are measured using a Kajaani FiberLab Fiber Analyzer as described herein.

In one example, the hardwood pulp fibers of the present invention comprise hardwood pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 13.90 μm and/or less than         13.80 μm and/or less than 13.70 μm and/or less than 13.60 μm         and/or less than 13.50 μm and/or less than 13.45 μm;     -   b. a Kajaani fiber cell wall thickness of less than 5.98 μm         and/or less than 5.97 μm and/or less than 5.96 μm and/or less         than 5.94 μm; and     -   c. a Kajaani millions of fibers/gram of greater than 24 millions         of fibers/gram and/or greater than 24.5 millions of fibers/gram         and/or greater than 25 millions of fibers/gram;

as measured using a Kajaani FiberLab Fiber Analyzer commercially available from Metso Automation, Kajaani Finland.

In another example, the hardwood pulp fibers of the present invention comprise tropical hardwood pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 14.05 μm and/or less than         14.00 μm and/or less than 13.95 μm and/or less than 13.90 μm         and/or less than 13.80 μm and/or less than 13.70 μm and/or less         than 13.60 μm and/or less than 13.50 μm and/or less than 13.45         μm;     -   b. a Kajaani fiber cell wall thickness of less than 5.98 μm         and/or less than 5.97 μm and/or less than 5.96 μm and/or less         than 5.94 μm;     -   c. a Kajaani millions of fibers/gram of greater than 22.7         millions of fibers/gram and/or greater than 23 millions of         fibers/gram and/or greater than 23.5 millions of fibers/gram         and/or greater than 24 millions of fibers/gram and/or 24.5         millions of fibers/gram and/or greater than 25 millions of         fibers/gram;     -   d. a Kajaani fiber length of less than 0.64 mm and/or less than         0.60 mm and/or less than 0.57 mm and/or less than 0.55 mm and/or         less than 0.53 mm and/or to about 0.40 mm and/or to about 0.45         mm and/or to about 0.50 mm and/or to about 0.52 mm; and     -   e. a ratio of Kajaani fiber length (μm) to Kajaani fiber width         (μm) of less than 45 and/or less than 43 and/or less than 41;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

In still another example, the hardwood pulp fibers of the present invention comprise eucalyptus pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 14.15 μm and/or less than         14.10 μm and/or less than 14.05 μm and/or less than 14.00 μm         and/or less than 13.95 μm and/or less than 13.90 μm and/or less         than 13.80 μm and/or less than 13.70 μm and/or less than 13.60         μm and/or less than 13.50 μm and/or less than 13.45 μm;     -   b. a Kajaani fiber cell wall thickness of less than 6.15 μm         and/or less than 6.10 μm and/or less than 6.05 μm and/or less         than 6.00 μm and/or less than 5.98 μm and/or less than 5.97 μm         and/or less than 5.96 μm and/or less than 5.94 μm;     -   c. a Kajaani millions of fibers/gram of greater than 20.5         millions of fibers/gram and/or greater than 21 millions of         fibers/gram and/or greater than 21.5 millions of fibers/gram         and/or greater than 22 millions of fibers/gram and/or greater         than 22.5 millions of fibers/gram and/or greater than 23         millions of fibers/gram and/or greater than 23.5 millions of         fibers/gram and/or greater than 24 millions of fibers/gram         and/or 24.5 millions of fibers/gram and/or greater than 25         millions of fibers/gram;     -   d. a Kajaani fiber length of less than 0.64 mm and/or less than         0.60 mm and/or less than 0.57 mm and/or less than 0.55 mm and/or         less than 0.53 mm and/or to about 0.40 mm and/or to about 0.45         mm and/or to about 0.50 mm and/or to about 0.52 mm; and     -   e. a ratio of Kajaani fiber length (μm) to Kajaani fiber width         (μm) of less than 45 and/or less than 43 and/or less than 41;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

In one example, the hardwood pulp fibers and/or tropical hardwood pulp fibers and/or eucalyptus pulp fibers of the present invention exhibit a Kajaani Fiber Collapse Ratio of greater than 0.050 and/or greater than 0.052 to less than 0.078 and/or less than 0.075 and/or less than 0.070 and/or less than 0.065 and/or less than 0.060 as measured using a Kajaani FiberLab Fiber Analyzer commercially available from Metso Automation, Kajaani Finland.

In one example, the hardwood pulp fibers and/or tropical hardwood pulp fibers and/or eucalyptus pulp fibers of the present invention exhibit a Kajaani Fiber Coarseness of less than 0.075 mg/m and/or 0.073 mg/m or less and/or to about 0.010 mg/m and/or to about 0.020 mg/m and/or to about 0.030 mg/m and/or to about 0.040 mg/m and/or to about 0.050 mg/m and/or to about 0.060 mg/m and/or greater than 0.068 mg/m as measured using a Kajaani FiberLab Fiber Analyzer commercially available from Metso Automation, Kajaani Finland.

Table 1 below shows a comparison of fiber morphology for an example of a hardwood pulp fiber of the present invention, which is a tropical hardwood pulp fiber, namely, a eucalyptus pulp fiber (eucalyptus also referred to as euc) useful in the present invention and other known hardwood pulp fibers, including other eucalyptus pulp fibers, an acacia pulp fiber, which is a tropical hardwood pulp fiber, and a maple pulp fiber, which is a northern hardwood pulp fiber.

TABLE 1 Invention Suzano Fibria Northern Euc Euc Euc Euc Nitens Hardwood Property Fiber Fiber Fiber Acacia Fiber Fiber Maple Fiber Kajaani Fiber 0.54 0.65 0.72 0.65 0.66 0.51 Length (mm) Kajaani Fiber 13.42 14.16 14.56 14.06 14.3 13.95 Width (μm) Ratio of 40 46 49 46 46 36 Kajaani Fiber Length (μm) to Kajaani Fiber Width (μm) Kajaani Cell 5.92 6.30 6.48 5.98 6.16 6.40 Wall Thickness (μm) Kajaani 0.073 0.084 0.085 0.068 0.075 0.082 Coarseness (mg/m) Kajaani 25.4 18.3 16.3 22.6 20.2 23.9 Millions of Fibers/Gram Kajaani Fiber 0.053 0.048 0.049 0.092 0.080 0.026 Collapse Ratio

The hardwood pulp fibers of the present invention may be obtained from one or more hardwood pulp trees and/or tropical hardwood pulp trees and/or eucalyptus pulp trees that are a source of the hardwood pulp fibers of the present invention via a suitable pulping process known in the art. The pulping process may provide a hardwood pulp fiber composition comprising a plurality of hardwood pulp fibers. In one example, eucalyptus pulp fibers of the present invention are extracted from a eucalyptus pulp fiber composition commercially available from Suzano Pulp & Paper under the trade name Suzano Mucuri, which comprises a mixture of eucalyptus pulp fibers including a relatively small amount by weight of the eucalyptus pulp fiber of the present invention.

Hardwood Pulp Fiber Composition

The hardwood pulp fibers of the present invention may be in the form of a hardwood pulp fiber composition comprising 20% or greater and/or 30% or greater and/or 40% or greater and/or 50% or greater and/or 60% or greater and/or 70% or greater and/or 80% or greater and/or 90% or greater and/or up to 100% by weight of hardwood pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 13.90 μm and/or less than         13.80 μm and/or less than 13.70 μm and/or less than 13.60 μm         and/or less than 13.50 μm and/or less than 13.45 μm;     -   b. a Kajaani fiber cell wall thickness of less than 5.98 μm         and/or less than 5.97 μm and/or less than 5.96 μm and/or less         than 5.94 μm; and     -   c. a Kajaani millions of fibers/gram of greater than 24 millions         of fibers/gram and/or greater than 24.5 millions of fibers/gram         and/or greater than 25 millions of fibers/gram;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

The tropical hardwood pulp fibers of the present invention may be in the form of a tropical hardwood pulp fiber composition comprising 20% or greater and/or 30% or greater and/or 40% or greater and/or 50% or greater and/or 60% or greater and/or 70% or greater and/or 80% or greater and/or 90% or greater and/or up to 100% by weight of tropical hardwood pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 14.05 μm and/or less than         14.00 μm and/or less than 13.95 μm and/or less than 13.90 μm         and/or less than 13.80 μm and/or less than 13.70 μm and/or less         than 13.60 μm and/or less than 13.50 μm and/or less than 13.45         μm;     -   b. a Kajaani fiber cell wall thickness of less than 5.98 μm         and/or less than 5.97 μm and/or less than 5.96 μm and/or less         than 5.94 μm;     -   c. a Kajaani millions of fibers/gram of greater than 22.7         millions of fibers/gram and/or greater than 23 millions of         fibers/gram and/or greater than 23.5 millions of fibers/gram         and/or greater than 24 millions of fibers/gram and/or 24.5         millions of fibers/gram and/or greater than 25 millions of         fibers/gram;     -   d. a Kajaani fiber length of less than 0.64 mm and/or less than         0.60 mm and/or less than 0.57 mm and/or less than 0.55 mm and/or         less than 0.53 mm and/or to about 0.40 mm and/or to about 0.45         mm and/or to about 0.50 mm and/or to about 0.52 mm; and     -   e. a ratio of Kajaani fiber length (μm) to Kajaani fiber width         (μm) of less than 45 and/or less than 43 and/or less than 41;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

The eucalyptus pulp fibers of the present invention may be in the form of a eucalyptus pulp fiber composition comprising 20% or greater and/or 30% or greater and/or 40% or greater and/or 50% or greater and/or 60% or greater and/or 70% or greater and/or 80% or greater and/or 90% or greater and/or up to 100% by weight of eucalyptus pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 14.15 μm and/or less than         14.10 μm and/or less than 14.05 μm and/or less than 14.00 μm         and/or less than 13.95 μm and/or less than 13.90 μm and/or less         than 13.80 μm and/or less than 13.70 μm and/or less than 13.60         μm and/or less than 13.50 μm and/or less than 13.45 μm;     -   b. a Kajaani fiber cell wall thickness of less than 6.15 μm         and/or less than 6.10 μm and/or less than 6.05 μm and/or less         than 6.00 μm and/or less than 5.98 μm and/or less than 5.97 μm         and/or less than 5.96 μm and/or less than 5.94 μm;     -   c. a Kajaani millions of fibers/gram of greater than 20.5         millions of fibers/gram and/or greater than 21 millions of         fibers/gram and/or greater than 21.5 millions of fibers/gram         and/or greater than 22 millions of fibers/gram and/or greater         than 22.5 millions of fibers/gram and/or greater than 23         millions of fibers/gram and/or greater than 23.5 millions of         fibers/gram and/or greater than 24 millions of fibers/gram         and/or 24.5 millions of fibers/gram and/or greater than 25         millions of fibers/gram;     -   d. a Kajaani fiber length of less than 0.64 mm and/or less than         0.60 mm and/or less than 0.57 mm and/or less than 0.55 mm and/or         less than 0.53 mm and/or to about 0.40 mm and/or to about 0.45         mm and/or to about 0.50 mm and/or to about 0.52 mm; and     -   e. a ratio of Kajaani fiber length (μm) to Kajaani fiber width         (μm) of less than 45 and/or less than 43 and/or less than 41;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

Processes for Making the Hardwood Pulp Fiber Composition

The hardwood pulp fiber composition of the present invention may be derived by adjusting the composition of available hardwood fiber pulp mixtures. In one example, a hardwood pulp fiber composition of the present invention is obtained using a process for comprising the steps of:

-   -   a. providing a hardwood pulp fiber composition comprising less         than 20% by weight of hardwood pulp fibers that exhibit one or         more of the following properties:         -   i. a Kajaani fiber width of less than 13.90 μm and/or less             than 13.80 μm and/or less than 13.70 μm and/or less than             13.60 μm and/or less than 13.50 μm and/or less than 13.45             μm;         -   ii. a Kajaani fiber cell wall thickness of less than 5.98 μm             and/or less than 5.97 μm and/or less than 5.96 μm and/or             less than 5.94 μm; and         -   iii. a Kajaani millions of fibers/gram of greater than 24             millions of fibers/gram and/or greater than 24.5 millions of             fibers/gram and/or greater than 25 millions of fibers/gram;         -   as measured using a Kajaani FiberLab Fiber Analyzer             commercially available from Metso Automation, Kajaani             Finland; and     -   b. adjusting the weight percent of the hardwood pulp fibers such         that a hardwood pulp fiber composition comprising 20% or greater         by weight of hardwood pulp fibers that exhibit one or more of         the following properties:         -   i. a Kajaani fiber width of less than 13.90 μm and/or less             than 13.80 μm and/or less than 13.70 μm and/or less than             13.60 μm and/or less than 13.50 μm and/or less than 13.45             μm;         -   ii. a Kajaani fiber cell wall thickness of less than 5.98 μm             and/or less than 5.97 μm and/or less than 5.96 μm and/or             less than 5.94 μm; and         -   iii. a Kajaani millions of fibers/gram of greater than 24             millions of fibers/gram and/or greater than 24.5 millions of             fibers/gram and/or greater than 25 millions of fibers/gram;         -   as measured using a Kajaani FiberLab Fiber Analyzer             commercially available from Metso Automation, Kajaani             Finland is formed.

In another example, a tropical hardwood pulp fiber composition of the present invention is obtained using a process for comprising the steps of:

-   -   a. providing a tropical hardwood pulp fiber composition         comprising less than 20% by weight of tropical hardwood pulp         fibers that exhibit one or more of the following properties:         -   i. a Kajaani fiber width of less than 14.05 μm and/or less             than 14.00 μm and/or less than 13.95 μm and/or less than             13.90 μm and/or less than 13.80 μm and/or less than 13.70 μm             and/or less than 13.60 μm and/or less than 13.50 μm and/or             less than 13.45 μm;         -   ii. a Kajaani fiber cell wall thickness of less than 5.98 μm             and/or less than 5.97 μm and/or less than 5.96 μm and/or             less than 5.94 μm;         -   iii. a Kajaani millions of fibers/gram of greater than 22.7             millions of fibers/gram and/or greater than 23 millions of             fibers/gram and/or greater than 23.5 millions of fibers/gram             and/or greater than 24 millions of fibers/gram and/or 24.5             millions of fibers/gram and/or greater than 25 millions of             fibers/gram;         -   iv. a Kajaani fiber length of less than 0.64 mm and/or less             than 0.60 mm and/or less than 0.57 mm and/or less than 0.55             mm and/or less than 0.53 mm and/or to about 0.40 mm and/or             to about 0.45 mm and/or to about 0.50 mm and/or to about             0.52 mm; and         -   v. a ratio of Kajaani fiber length (μm) to Kajaani fiber             width (μm) of less than 45 and/or less than 43 and/or less             than 41;         -   as measured using a Kajaani FiberLab Fiber Analyzer             commercially available from Metso Automation, Kajaani             Finland; and     -   b. adjusting the weight percent of the tropical hardwood pulp         fibers such that a tropical hardwood pulp fiber composition         comprising 20% or greater by weight of tropical hardwood pulp         fibers that exhibit one or more of the following properties:         -   i. a Kajaani fiber width of less than 14.05 μm and/or less             than 14.00 μm and/or less than 13.95 μm and/or less than             13.90 μm and/or less than 13.80 μm and/or less than 13.70 μm             and/or less than 13.60 μm and/or less than 13.50 μm and/or             less than 13.45 μm;         -   ii. a Kajaani fiber cell wall thickness of less than 5.98 μm             and/or less than 5.97 μm and/or less than 5.96 μm and/or             less than 5.94 μm;         -   iii. a Kajaani millions of fibers/gram of greater than 22.7             millions of fibers/gram and/or greater than 23 millions of             fibers/gram and/or greater than 23.5 millions of fibers/gram             and/or greater than 24 millions of fibers/gram and/or 24.5             millions of fibers/gram and/or greater than 25 millions of             fibers/gram;         -   iv. a Kajaani fiber length of less than 0.64 mm and/or less             than 0.60 mm and/or less than 0.57 mm and/or less than 0.55             mm and/or less than 0.53 mm and/or to about 0.40 mm and/or             to about 0.45 mm and/or to about 0.50 mm and/or to about             0.52 mm; and         -   v. a ratio of Kajaani fiber length (μm) to Kajaani fiber             width (μm) of less than 45 and/or less than 43 and/or less             than 41;         -   as measured using a Kajaani FiberLab Fiber Analyzer             commercially available from Metso Automation, Kajaani             Finland is formed.

In another example, a eucalyptus pulp fiber composition of the present invention is obtained using a process for comprising the steps of:

-   -   a. providing a eucalyptus pulp fiber composition, for example a         eucalyptus pulp fiber composition from Suzano Pulp and Paper         under the trade name Suzano Mucuri, comprising less than 20% by         weight of eucalyptus pulp fibers that exhibit one or more of the         following properties:         -   i. a Kajaani fiber width of less than 14.15 μm and/or less             than 14.10 μm and/or less than 14.05 μm and/or less than             14.00 μm and/or less than 13.95 μm and/or less than 13.90 μm             and/or less than 13.80 μm and/or less than 13.70 μm and/or             less than 13.60 μm and/or less than 13.50 μm and/or less             than 13.45 μm;         -   ii. a Kajaani fiber cell wall thickness of less than 6.15 μm             and/or less than 6.10 μm and/or less than 6.05 μm and/or             less than 6.00 μm and/or less than 5.98 μm and/or less than             5.97 μm and/or less than 5.96 μm and/or less than 5.94 μm;         -   iii. a Kajaani millions of fibers/gram of greater than 20.5             millions of fibers/gram and/or greater than 21 millions of             fibers/gram and/or greater than 21.5 millions of fibers/gram             and/or greater than 22 millions of fibers/gram and/or             greater than 22.5 millions of fibers/gram and/or greater             than 23 millions of fibers/gram and/or greater than 23.5             millions of fibers/gram and/or greater than 24 millions of             fibers/gram and/or 24.5 millions of fibers/gram and/or             greater than 25 millions of fibers/gram;         -   iv. a Kajaani fiber length of less than 0.64 mm and/or less             than 0.60 mm and/or less than 0.57 mm and/or less than 0.55             mm and/or less than 0.53 mm and/or to about 0.40 mm and/or             to about 0.45 mm and/or to about 0.50 mm and/or to about             0.52 mm; and         -   v. a ratio of Kajaani fiber length (μm) to Kajaani fiber             width (μm) of less than 45 and/or less than 43 and/or less             than 41;         -   as measured using a Kajaani FiberLab Fiber Analyzer             commercially available from Metso Automation, Kajaani             Finland; and     -   b. adjusting the weight percent of the eucalyptus pulp fibers         such that a eucalyptus pulp fiber composition comprising 20% or         greater by weight of eucalyptus pulp fibers that exhibit one or         more of the following properties:         -   i. a Kajaani fiber width of less than 14.15 μm and/or less             than 14.10 μm and/or less than 14.05 μm and/or less than             14.00 μm and/or less than 13.95 μm and/or less than 13.90 μm             and/or less than 13.80 μm and/or less than 13.70 μm and/or             less than 13.60 μm and/or less than 13.50 μm and/or less             than 13.45 μm;         -   ii. a Kajaani fiber cell wall thickness of less than 6.15 μm             and/or less than 6.10 μm and/or less than 6.05 μm and/or             less than 6.00 μm and/or less than 5.98 μm and/or less than             5.97 μm and/or less than 5.96 μm and/or less than 5.94 μm;         -   iii. a Kajaani millions of fibers/gram of greater than 20.5             millions of fibers/gram and/or greater than 21 millions of             fibers/gram and/or greater than 21.5 millions of fibers/gram             and/or greater than 22 millions of fibers/gram and/or             greater than 22.5 millions of fibers/gram and/or greater             than 23 millions of fibers/gram and/or greater than 23.5             millions of fibers/gram and/or greater than 24 millions of             fibers/gram and/or 24.5 millions of fibers/gram and/or             greater than 25 millions of fibers/gram;         -   iv. a Kajaani fiber length of less than 0.64 mm and/or less             than 0.60 mm and/or less than 0.57 mm and/or less than 0.55             mm and/or less than 0.53 mm and/or to about 0.40 mm and/or             to about 0.45 mm and/or to about 0.50 mm and/or to about             0.52 mm; and         -   v. a ratio of Kajaani fiber length (μm) to Kajaani fiber             width (μm) of less than 45 and/or less than 43 and/or less             than 41;         -   as measured using a Kajaani FiberLab Fiber Analyzer             commercially available from Metso Automation, Kajaani             Finland is formed.

Fibrous Structures

The fibrous structures of the present invention may comprise greater than 20% and/or greater than 30% and/or greater than 40% and/or greater than 50% and/or greater than 75% and/or greater than 90% and/or 100% or less by weight on a dry fiber basis of pulp fibers.

In one example, the fibrous structure of the present invention comprises 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of hardwood pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 13.90 μm and/or less than         13.80 μm and/or less than 13.70 μm and/or less than 13.60 μm         and/or less than 13.50 μm and/or less than 13.45 μm;     -   b. a Kajaani fiber cell wall thickness of less than 5.98 μm         and/or less than 5.97 μm and/or less than 5.96 μm and/or less         than 5.94 μm; and     -   c. a Kajaani millions of fibers/gram of greater than 24 millions         of fibers/gram and/or greater than 24.5 millions of fibers/gram         and/or greater than 25 millions of fibers/gram;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

In another example, the fibrous structure of the present invention comprises 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of tropical hardwood pulp fibers, for example tropical hardwood pulp fibers selected from the group consisting of acacia pulp fibers, eucalyptus pulp fibers, and mixtures thereof, that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 14.05 μm and/or less than         14.00 μm and/or less than 13.95 μm and/or less than 13.90 μm         and/or less than 13.80 μm and/or less than 13.70 μm and/or less         than 13.60 μm and/or less than 13.50 μm and/or less than 13.45         μm;     -   b. a Kajaani fiber cell wall thickness of less than 5.98 μm         and/or less than 5.97 μm and/or less than 5.96 μm and/or less         than 5.94 μm;     -   c. a Kajaani millions of fibers/gram of greater than 22.7         millions of fibers/gram and/or greater than 23 millions of         fibers/gram and/or greater than 23.5 millions of fibers/gram         and/or greater than 24 millions of fibers/gram and/or 24.5         millions of fibers/gram and/or greater than 25 millions of         fibers/gram;     -   d. a Kajaani fiber length of less than 0.64 mm and/or less than         0.60 mm and/or less than 0.57 mm and/or less than 0.55 mm and/or         less than 0.53 mm and/or to about 0.40 mm and/or to about 0.45         mm and/or to about 0.50 mm and/or to about 0.52 mm; and     -   e. a ratio of Kajaani fiber length (μm) to Kajaani fiber width         (μm) of less than 45 and/or less than 43 and/or less than 41;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

In another example, the fibrous structure of the present invention comprises 1% and/or 3% and/or 5% or greater, for example greater than 5%, by weight of eucalyptus pulp fibers that exhibit one or more of the following properties:

-   -   a. a Kajaani fiber width of less than 14.15 μm and/or less than         14.10 μm and/or less than 14.05 μm and/or less than 14.00 μm         and/or less than 13.95 μm and/or less than 13.90 μm and/or less         than 13.80 μm and/or less than 13.70 μm and/or less than 13.60         μm and/or less than 13.50 μm and/or less than 13.45 μm;     -   b. a Kajaani fiber cell wall thickness of less than 6.15 μm         and/or less than 6.10 μm and/or less than 6.05 μm and/or less         than 6.00 μm and/or less than 5.98 μm and/or less than 5.97 μm         and/or less than 5.96 μm and/or less than 5.94 μm;     -   c. a Kajaani millions of fibers/gram of greater than 20.5         millions of fibers/gram and/or greater than 21 millions of         fibers/gram and/or greater than 21.5 millions of fibers/gram         and/or greater than 22 millions of fibers/gram and/or greater         than 22.5 millions of fibers/gram and/or greater than 23         millions of fibers/gram and/or greater than 23.5 millions of         fibers/gram and/or greater than 24 millions of fibers/gram         and/or 24.5 millions of fibers/gram and/or greater than 25         millions of fibers/gram;     -   d. a Kajaani fiber length of less than 0.64 mm and/or less than         0.60 mm and/or less than 0.57 mm and/or less than 0.55 mm and/or         less than 0.53 mm and/or to about 0.40 mm and/or to about 0.45         mm and/or to about 0.50 mm and/or to about 0.52 mm; and     -   e. a ratio of Kajaani fiber length (μm) to Kajaani fiber width         (μm) of less than 45 and/or less than 43 and/or less than 41;     -   as measured using a Kajaani FiberLab Fiber Analyzer commercially         available from Metso Automation, Kajaani Finland.

In one example, the fibrous structures of the present invention comprise from greater than 5% and/or greater than 10% and/or greater than 15% and/or greater than 20% and/or to about 50% and/or to about 45% and/or to about 40% by weight of the hardwood pulp fibers and/or tropical hardwood pulp fibers and/or eucalyptus pulp fibers of the present invention.

In another example, the fibrous structures of the present invention comprise from greater than 50% and/or greater than 60% and/or greater than 70% and/or to about 100% and/or to about 90% and/or to about 80% by weight of the hardwood pulp fibers and/or tropical hardwood pulp fibers and/or eucalyptus pulp fibers of the present invention.

In one example, the fibrous structures of the present invention may exhibit a basis weight between about 10 g/m² to about 120 g/m² and/or from about 15 g/m² to about 110 g/m² and/or from about 20 g/m² to about 100 g/m² and/or from about 30 to 90 g/m². In addition, the sanitary tissue product of the present invention may exhibit a basis weight between about 40 g/m² to about 120 g/m² and/or from about 50 g/m² to about 110 g/m² and/or from about 55 g/m² to about 105 g/m² and/or from about 60 to 100 g/m² as measured according to the Basis Weight Test Method described herein.

In another example, the fibrous structures of the present invention may exhibit a basis weight of at least 21 g/m² and/or at least 23 g/m² and/or at least 25 g/m².

In addition to the hardwood pulp fibers and/or tropical hardwood pulp fibers and/or eucalyptus pulp fibers of the present invention, the fibrous structure may comprise other additives, such as wet strength additives (such as permanent and/or temporary wet strength additives), softening additives (such as silicones and/or quaternary ammonium compounds), solid additives (such as starch, clays), dry strength resins, wetting agents, lint resisting and/or reducing agents, absorbency-enhancing agents, immobilizing agents, especially in combination with emollient lotion compositions, antiviral agents including organic acids, antibacterial agents, polyol polyesters, antimigration agents, polyhydroxy plasticizers, and mixtures thereof. Such other additives may be added to the fiber furnish, the embryonic fibrous web and/or the fibrous structure. Such additives may be present in the fibrous structure at any level based on the dry weight of the fibrous structure. In one example, an additive may be present in the fibrous structure at a level of from about 0.001 to about 50% and/or from about 0.001 to about 20% and/or from about 0.01 to about 5% and/or from about 0.03 to about 3% and/or from about 0.1 to about 1.0% by weight, on a dry fibrous structure basis.

In one example, a fibrous structure of the present invention comprises a softening additive, for example silicone. In another example, the fibrous structure of the present invention comprises a softening additive, for example a quaternary ammonium compound.

In another example, the fibrous structure of the present invention comprises a through-air-dried fibrous structure.

In still another example, the fibrous structure of the present inveniton comprises a creped fibrous structure.

In yet another example, the fibrous structure of the present invention comprises an uncreped fibrous structure.

The fibrous structures of the present invention may further comprise other hardwood pulp fibers that exhibit Kajaani fiber widths of 13.90 μm or greater and/or other tropical hardwood pulp fibers that exhibit Kajaani fiber widths of 14.05 μm or greater and/or other eucalyptus pulp fibers that exhibit Kajaani fiber widths of 14.15 μm or greater as measured using a Kajaani FiberLab Fiber Analyzer commercially available from Metso Automation, Kajaani Finland.

In addition to hardwood pulp fibers of the present invention, the fibrous structures may comprise softwood pulp fibers. Suitable softwood pulp fibers include softwood pulp fibers selected from the group consisting of: Southern Softwood Kraft, Tropical Softwood Kraft and Northern Softwood Kraft, Tropical Softwood Kraft, and mixtures thereof.

The fibrous structures of the present invention may be subjected to any suitable post processing including, but not limited to, printing, embossing, calendaring, slitting, folding, combining with other fibrous structures, and the like.

A single- or multi-ply sanitary tissue product may comprise one or more fibrous structures of the present invention. The sanitary tissue product may be in roll form.

Processes for Making Hardwood Pulp Fiber-Containing Fibrous Structures

Any suitable process for making fibrous structures known in the art may be used to make hardwood pulp fiber-containing fibrous structures of the present invention.

In one example, the hardwood pulp fiber-containing fibrous structures of the present invention are made by a wet laid fibrous structure making process.

In another example, the hardwood pulp fiber-containing fibrous structures of the present invention are made by an air laid fibrous structure making process.

In one example, a hardwood pulp fiber-containing fibrous structure is made by the process comprising the steps of: a) preparing a fiber furnish (slurry) by mixing a hardwood pulp fiber with water; b) depositing the fiber furnish on a foraminous forming surface to form an embryonic fibrous web; and c) drying the embryonic fibrous web.

In one example, a fiber furnish comprising a hardwood pulp fiber, such as a tropical hardwood pulp fiber, for example a eucalyptus pulp fiber, is deposited onto a foraminuous forming surface via a headbox.

Non-Limiting Example

The following example illustrates a non-limiting example for the preparation of a hardwood pulp fiber-containing fibrous structure of the present invention.

A sheet with 32%×33%×35% layering consist of fabric layer, center layer and wire layer. The entire sheet has 70% by weight on a dry fiber basis of eucalyptus pulp fibers of the present invention and 30% by weight on a dry fiber basis of northern softwood kraft (NSK) pulp fibers is made.

An aqueous slurry of the eucalyptus pulp fibers is prepared at about 3% by weight using a conventional repulper. Separately, an aqueous slurry of the NSK pulp fibers of about 3% by weight is made up using a conventional repulper.

In order to impart temporary wet strength to the finished fibrous structure, a 1% dispersion of a temporary wet strength additive (e.g., Parez® commercially available from Kemira) is prepared and is added to the NSK fiber stock pipe at a rate sufficient to deliver 0.3% temporary wet strength additive based on the dry weight of the NSK pulp fibers. The absorption of the temporary wet strength additive is enhanced by passing the treated NSK pulp fiber slurry through an in-line mixer.

The eucalyptus pulp fiber slurry is diluted with white water at the inlet of a fan pump to a consistency of about 0.15% based on the total weight of the eucalyptus pulp fiber slurry. The NSK pulp fibers, likewise, are diluted with white water at the inlet of a fan pump to a consistency of about 0.15% based on the total weight of the NSK pulp fiber slurry. The eucalyptus pulp fiber slurry and the NSK pulp fiber slurry are both directed to a layered headbox capable of maintaining the slurries as separate streams until they are deposited onto a forming fabric on the Fourdrinier.

“DC 2310” (Dow Corning, Midland, Mich.) antifoam is dripped into the wirepit to control foam to maintain white water levels of 10 ppm.

The paper making machine has a layered headbox with a top chamber, a center chamber, and a bottom chamber. The eucalyptus pulp fiber slurry is pumped through the top and bottom headbox chambers and, simultaneously, the NSK pulp fiber slurry is pumped through the center headbox chamber and delivered in superposed relation onto a Fourdrinier wire to form thereon a three-layer embryonic web, of which about 70% is made up of the eucalyptus pulp fibers and about 30% is made up of the NSK pulp fibers. Dewatering occurs through the Fourdrinier wire and is assisted by a deflector and vacuum boxes. The Fourdrinier wire is of a 5-shed, satin weave configuration having 87 machine-direction and 76 cross-machine-direction monofilaments per inch, respectively. The speed of the Fourdrinier wire is about 750 fpm (feet per minute).

The embryonic wet web is transferred from the Fourdrinier wire, at a fiber consistency of about 15% at the point of transfer, to a patterned drying fabric. The speed of the patterned drying fabric is about the same as the speed of the Fourdrinier wire. The drying fabric is designed to yield a pattern densified tissue with discontinuous low-density deflected areas arranged within a continuous network of high density (knuckle) areas. This drying fabric is formed by casting an impervious resin surface onto a fiber mesh supporting fabric. The supporting fabric is a 98×62 filament, dual layer mesh. The thickness of the resin cast is about 12 mils above the supporting fabric. A suitable process for making the patterned drying fabric is described in published application US 2004/0084167 A1.

Further de-watering is accomplished by vacuum assisted drainage until the web has a fiber consistency of about 30%.

While remaining in contact with the patterned drying fabric, the web is pre-dried by air blow-through pre-dryers to a fiber consistency of about 65% by weight.

After the pre-dryers, the semi-dry web is transferred to the Yankee dryer and adhered to the surface of the Yankee dryer with a sprayed creping adhesive. The creping adhesive is an aqueous dispersion with the actives consisting of about 22% polyvinyl alcohol, about 11% CREPETROL A3025, and about 67% CREPETROL R6390. CREPETROL A3025 and CREPETROL R6390 are commercially available from Hercules Incorporated of Wilmington, Del. The creping adhesive is delivered to the Yankee surface at a rate of about 0.15% adhesive solids based on the dry weight of the web. The fiber consistency is increased to about 97% before the web is dry creped from the Yankee with a doctor blade.

The doctor blade has a bevel angle of about 25 degrees and is positioned with respect to the Yankee dryer to provide an impact angle of about 81 degrees. The Yankee dryer is operated at a temperature of about 350° F. and a speed of about 800 fpm. The fibrous structure is wound in a roll using a surface driven reel drum having a surface speed of about 656 feet per minute. The fibrous structure may be subsequently converted into a two-ply sanitary tissue product having a basis weight of about 50 lbs/3000 ft².

Test Methods

Unless otherwise specified, all tests described herein including those described under the Definitions section and the following test methods are conducted on samples that have been conditioned in a conditioned room at a temperature of 23° C.±1.0° C. and a relative humidity of 50%±2% for a minimum of 2 hours prior to the test. The samples tested, unless otherwise specified, are “usable units.” “Usable units” as used herein means sheets, flats from roll stock, pre-converted flats, and/or single or multi-ply products. All tests are conducted under the same environmental conditions and in such conditioned room. Do not test samples that have defects such as wrinkles, tears, holes, and like. Samples conditioned as described herein are considered dry samples (such as “dry filaments”) for testing purposes. All instruments are calibrated according to manufacturer's specifications.

Basis Weight Test Method

Basis weight of a fibrous structure is measured on stacks of twelve usable units using a top loading analytical balance with a resolution of ±0.001 g. The balance is protected from air drafts and other disturbances using a draft shield. A precision cutting die, measuring 3.500 in±0.0035 in by 3.500 in±0.0035 in is used to prepare all samples.

With a precision cutting die, cut the samples into squares. Combine the cut squares to form a stack twelve samples thick. Measure the mass of the sample stack and record the result to the nearest 0.001 g.

The Basis Weight is calculated in lbs/3000 ft² or g/m² as follows:

Basis Weight=(Mass of stack)/[(Area of 1 square in stack)×(No.of squares in stack)]

For example,

Basis Weight (lbs/3000 ft²)=[[Mass of stack (g)/453.6 (g/lbs)]/[12.25 (in²)/144 (in²/ft²)×12]]×3000

or,

Basis Weight (g/m²)=Mass of stack (g)/[79.032 (cm²)/10,000 (cm²/m²)×12]

Report result to the nearest 0.1 lbs/3000 ft² or 0.1 g/m². Sample dimensions can be changed or varied using a similar precision cutter as mentioned above, so as at least 100 square inches of sample area in stack.

Kajaani FiberLab Fiber Analyzer Test Method Instrument Start-Up:

-   -   1. Turn on Kajaani FiberLab Fiber Analyzer unit first, then         computer and monitor.     -   2. Start FiberLab program on computer.

Instrument Operation:

-   -   1. File New (or click on New File icon)     -   2. “New Fiber Analysis” screen pops up.         -   a. Sample Point: select the folder you would like data             stored in (to add a new folder see “Adding a New Folder”         -   b. Name: add condition or sample name/identifier here         -   c. Date         -   d. Time         -   e. Sample Weight: mg of dry fiber in the 50 ml sample (can             leave blank if NOT measuring for coarseness). This is the             number calculated in #10 of Sample Prep below.     -   3. Make sure 50 ml of sample is placed in a “Kajaani beaker” and         click “Start”     -   4. Optional: Distribution→Measured Values         -   a. Fibers: the final count of measured fibers should be at             least 10,000         -   b. Fibers/sec: this number must stay below 70 fibers/sec or             the sample will automatically be diluted. If the sample is             diluted during an analysis, the coarseness value will be             invalid and will need to be discarded.     -   5. A bar indicating the measurement status of a sample appears         on the computer monitor. Do not start an analysis until the         indicated status is “Wait State”. When the analysis is         completed, wait for “Wait State” to appear, then close the “New         Fiber Analysis” window. You can now repeat #1-3/4     -   6. When finished with all samples, close the FiberLab program         before turning off the Kajaani FiberLab analyzer unit.     -   7. Shutdown computer.

Sample Preparation:

Target Sample Size:

Softwood: 4 mg/50 ml→160 mg BD in 2000 ml (−170-175 mg from sheet)

Hardwood: 1 mg/50 ml→40 mg BD in 2000 ml (−40-45 mg from sheet)

-   -   1. For n=3 analysis, weigh and record weight of sample torn         (avoiding cut edges) from 3 different pulp sheets of same sample         using guidelines above for sample size. Place weighed samples         into a suitable container for soaking of pulp.     -   2. Using the 3 sheets that samples were torn from, perform         moisture content analysis. Note: This step can be skipped if         coarseness measurement is not required.     -   3. Calculate the actual bone dry weight of the samples weighed         in #1, by using the average moisture determined in #2.     -   4. Allow pulp samples to soak in water for 10-15 minutes.     -   5. Place 1^(st) sample and soaking water into the Kajaani manual         disintegrator. Fill disintegrator up to 250 ml mark with more         water.     -   6. Using the “hand dasher”, plunge up and down until sample is         separated into individual fibers.     -   7. Transfer sample to a 2000 ml volumetric flask. Make sure to         wash off and collect any fibers that may have adhered to the         dasher.     -   8. Dilute up to 2000 ml mark. It is important to be as precise         as possible for repeatable coarseness results.     -   9. Take a 50 ml aliquot and place into a Kajaani beaker. Place         beaker on the sampler unit.     -   10. Calculate the mg of BD pulp in 50 ml aliquot         -   a. (BD mg of sample/2000 ml)×50 ml     -   11. Begin Step #1 above in Instrument Operation

The water used in this method is City of Cincinnati Water or equivalent having the following properties: Total Hardness=155 mg/L as CaCO₃; Calcium content=33.2 mg/L; Magnesium content=17.5 mg/L; Phosphate content=0.0462

Adding a New Folder to Sample Point Menu:

-   -   1. Settings→Common Settings→Sample Folders         -   a. Type in name of new folder→Add→OK         -   Note: You must close the FiberLab program and re-open             program to see the new folder appear in the menu.

Collecting Data in Excel File:

-   -   1. Start FiberLab's Collect 1.12 program.     -   2. Open Windows Explorer (not to full screen you must be able to         see both the Explorer and the Collect windows.     -   3. In Windows Explorer . . . Select folder that data was stored         in     -   4. Highlight data to be put in Excel→right click on Copy→drag         highlighted samples to the Collect window→Save text     -   5. Click “Save In” menu bar and select “My briefcase”. Open the         2007 folder, type in file name and click Save. A message will         appear saying the selected samples have been saved. Click OK         (the sample names will disappear from the Collect window.     -   6. Open Excel. Then . . . Open→Look In “My Briefcase”→2007→at         bottom, select “All Files (*.*)” in the “Files of Type” bar→find         text file just saved and open→click thru the Text Import Wizard         screens (next, next, finish)

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

What is claimed is:
 1. A fibrous structure comprising about 5% or greater by weight of a eucalyptus pulp fiber that exhibits a Kajaani fiber width of less than 14.15 μm.
 2. The fibrous structure according to claim 1 wherein the fibrous structure comprises greater than 10% by weight of the eucalyptus pulp fiber.
 3. The fibrous structure according to claim 1 wherein the fibrous structure comprises greater than 5% to about 50% by weight of the eucalyptus pulp fiber.
 4. The fibrous structure according to claim 1 wherein the fibrous structure comprises greater than 50% by weight of the eucalyptus pulp fiber.
 5. The fibrous structure according to claim 1 wherein the fibrous structure comprises greater than 50% to about 100% by weight of the eucalyptus pulp fiber.
 6. The fibrous structure according to claim 1 wherein the eucalyptus pulp fiber exhibits a Kajaani fiber width of less than 14.10 μm.
 7. The fibrous structure according to claim 1 wherein the eucalyptus pulp fiber exhibits a Kajaani fibers/gram of greater than 20.5 millions of fibers/gram.
 8. The fibrous structure according to claim 1 wherein the fibrous structure further comprises an additive selected from the group consisting of: permanent wet strength additives, temporary wet strength additives, softening additives, starch, clay, dry strength resins, wetting agents, lint resisting agents, absorbency-enhancing agents, immobilizing agents, lotion compositions, antiviral agents, antibacterial agents, polyol polyesters, antimigration agents, polyhydroxy plasticizers, and mixtures thereof.
 9. The fibrous structure according to claim 8 wherein the softening additives comprise a silicone.
 10. The fibrous structure according to claim 8 wherein the softening additives comprise a quaternary ammonium compound.
 11. The fibrous structure according to claim 1 wherein the fibrous structure comprises a through-air-dried fibrous structure.
 12. The fibrous structure according to claim 1 wherein the fibrous structure comprises a creped fibrous structure.
 13. The fibrous structure according to claim 1 wherein the fibrous structure comprises an uncreped fibrous structure.
 14. The fibrous structure according to claim 1 wherein the fibrous structure exhibits a basis weight of greater than 10 gsm to about 120 gsm.
 15. The fibrous structure according to claim 1 wherein the fibrous structure further comprises other hardwood pulp fibers that exhibit Kajaani fiber widths of 14.15 μm or greater.
 16. The fibrous structure according to claim 1 wherein the fibrous structure further comprises softwood pulp fibers.
 17. The fibrous structure according to claim 16 wherein the softwood pulp fibers are selected from the group consisting of: Southern Softwood Kraft, Tropical Softwood Kraft and Northern Softwood Kraft, Tropical Softwood Kraft, and mixtures thereof.
 18. A single- or multi-ply sanitary tissue product comprising a fibrous structure according to claim
 1. 19. The sanitary tissue product according to claim 18 wherein the sanitary tissue product is in roll form.
 20. A hardwood pulp fiber composition comprising: a. 20% or greater by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber width of less than 14.15 μm; and b. 80% or less by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber width of 14.15 μm or greater.
 21. The hardwood pulp fiber composition according to claim 20 wherein the hardwood pulp fiber composition comprises 30% or greater by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber width of less than 14.15 μm.
 22. The hardwood pulp fiber composition according to claim 21 wherein the hardwood pulp fiber composition comprises 50% to about 100% by weight of eucalyptus pulp fibers that exhibit a Kajaani fiber width of less than 14.15 μm. 